In Society of Automotive Engineers (SAE) paper No. 930650 entitled "A Complete Frontal Crash Sensor System-I", by Breed et al, which is incorporated herein by reference, the authors conclude that airbag crash sensors mounted in the crush zone are necessary for the proper sensing of airbag-required frontal crashes. They also conclude that such sensors should sense crashes to all portions of the front of the vehicle and that sensors which sense the crush of the vehicle are preferred. The theory of crush sensing is presented in the above-referenced U.S. patents and patent applications and in SAE paper No. 920122 entitled, "Performance of a Crush Sensor for Use with Automotive Airbag Systems", by Breed et al, which is incorporated herein by reference.
The tape switch and rod-in-tube crush sensors described in the above-referenced U.S. patents and patent applications, have performed successfully on various staged vehicle frontal crashes into barriers and poles. These sensors are generally not sufficient for sensing side impacts as discussed in Breed, D. S., Sanders, W. T. and Castelli, V., "Sensing Side Impacts", Society of Automotive Engineers (SAE) paper No. 940561, 1994, however, they can be successful when used in conjunction with a passenger compartment mounted electronic sensor or as a safing sensor. Similarly, they are also being considered when a deployable device, such as an airbag, is used for rear impacts.
Other technical papers which provide pertinent background information to this invention include:
1. Breed, D. S., Castelli, V. "Problems in Design and Engineering of Air Bag Systems", Society of Automotive Engineers paper No. 880724, 1988. PA1 2. Breed, D. S., Castelli, V. "Trends in Sensing Frontal Impacts", Society of Automotive Engineers paper No. 890750, 1989. PA1 3. Castelli, V., Breed, D. S. "Trends in Sensing Side Impacts", Society of Automotive Engineers paper No. 890603, 1989. PA1 4. Breed, D. S., Castelli, V. and Shokoohi, F. "Are Barrier Crashes Sufficient for Evaluating Air Bag Sensor Performance?", Society of Automotive Engineers paper No. 900548, 1990. PA1 5. Breed, D. S., Sanders, W. T. and Castelli, V. "A Critique of Single Point Crash Sensing", Society of Automotive Engineers paper No. 920124. 1992. PA1 6. Breed, D. S., Sanders, W. T. and Castelli, V. "Performance of a Crush Sensor for Use with Automobile airbag Systems", Society of Automotive Engineers paper No. 920122, 1992. PA1 7. Shokoohi, F., Sanders, W. T., Castelli, V., and Breed, D. S. "Cross Axis Specifications For Crash Sensors". Automotive Technologies International Report, ATI 12004, 1991. Society of Automotive Engineers paper No. 930651, 1993. PA1 8. Breed, D. S., Sanders, W. T. and Castelli, V. "A complete Frontal Crash Sensor System-I", Society of Automotive Engineers paper No. 930650, 1993. PA1 9. Breed, D. S. and Sanders, W. T. "Using Vehicle Deformation to Sense Crashes", Presented at the International Body and Engineering Conference, Detroit Mich., 1993. PA1 10. Breed, D. S., Sanders, W. T. and Castelli, V., "A complete Frontal Crash Sensor System-II", Proceedings Enhanced Safety of Vehicles Conference, Munich, 1994, Published by the U.S. Department of Transportation, National Highway Traffic Safety Administration, Washington, D.C. PA1 11. Breed, D. S., Sanders, W. T. and Castelli, V., "Sensing Side Impacts", Society of Automotive Engineers paper No. 940561, 1994. PA1 12. Breed, D. S., "Side Impact Airbag System Technology", Presented at the International Body and Engineering Conference, Detroit Mich., 1994. PA1 1) To provide a single sensor which will sense all airbag desired crashes involving the either the front, rear or a side of the vehicle. PA1 2) To provide a sensor which is much longer than it is wide or thick thus permitting it to sense crashes over a large area while occupying a relatively small space. PA1 3) To provide a sensor which can be easily shaped so to be properly placed at the CSZ boundary across the entire front or rear of the vehicle. PA1 4) To provide a crush sensor where the deformation required to trigger the sensor can be varied along the length of the sensor. PA1 5) To provide a sensor to be used in conjunction with an electronic passenger compartment mounted sensor which will trigger on all of the airbag desired crashes which are missed by the electronic passenger compartment mounted sensor alone for either frontal, side or rear impacts. PA1 6) To provide a simple and convenient sensor system consisting of a single discriminating sensor mounted at the CSZ boundary and a single arming sensor mounted in the passenger compartment for frontal and/or rear impacts. PA1 7) To provide a sensor which remains closed after it triggers during a crash. PA1 8) To provide a hermetically sealed crush sensing crash sensor. PA1 9) To provide a crash sensor which has a hermetically scaled integral connector thereby eliminating the need for wires to be connected inside the sensor housing. PA1 10) To provide a crush switch type crash sensor which does not require a strong mounting structure. PA1 11) To provide a sensor which operates on bending.
Other relevant prior art includes U.S. Pat. No. 3,859,482 to Matsui which will now be discussed in some detail. Matsui shows various devices which respond to the force (pressure using Matsui's terminology) which accompanies a vehicle frontal crash when material in the extreme front of the vehicle, or the impacting object itself, impacts the force detecting device. Matsui also mentions, but does not illustrate, the use of his force detectors on the rear and the side of the vehicle. The Matsui devices discriminate crashes based on the magnitude of this force on the detecting device, which as stated in the patent, are in the order of tons (metric). Many devices are described in Matsui however the following generalizations apply:
1. The Matsui sensors are mechanical pressure (force) detecting devices. This is stated in the title of the patent and throughout, there is only discussion of pressure being applied directly to the sensor. Except in those cases where a tape switch or a rope is used as the forwardmost point on the vehicle, there is always associated with the device a "Presser Member" whose function is to apply force directly to the sensor. Most importantly, this is a device which determines the severity of a crash based on force where the force is in the order of metric tons.
As discussed in greater detail below, the devices disclosed in the instant invention arc displacement sensors not force sensors, they do not require toils of force to actuated, are never placed at the forward most point on the vehicle, a "Presser Member" is not required or used, and they are designed to function by bending and not by compression.
2. The Matsui sensors are used in combination with a high level deceleration detector. In all cases, the Matsui sensor is used in conjunction with an acceleration sensor. This sensor is a low level discriminating sensor which is different from the safing sensor used on most current airbag systems. The difference between these types of sensors is that the Matsui sensor is not used alone to discriminate the crash, that is to determine whether the crash requires deployment of an airbag. An additional discriminating sensor is required. By contrast, in conventional airbag systems, a safing or arming sensor is used to guard against electrical shorts in the sensor perhaps caused by vehicle maintenance. The safing sensor will trigger on pothole impacts for example. It is not intended to provide information as to the severity of the crash. This is not the case in the Matsui acceleration sensor which is used in series with a force sensor. This is clear by the illustrated embodiment in FIG. 29 which shows that the deceleration sensor requires a value of acceleration to trigger which is shown to be a substantial percent of the peak deceleration of curve A which is on the order of about 40 G's (see for example FIG. 1 of reference 1 above). In contrast, typical safing or arming sensors trigger on a deceleration of less than about 2 G's.
Again, as will be discussed in detail below, in contrast, the sensors of the present invention do not require a high level deceleration sensor or any deceleration sensor for that matter. When the sensors of this invention are used as discriminating sensors, a low level safing or arming sensor can optionally be used to provide electrical isolation of the inflator initiator so that momentary electrical shorts do not cause deployment of the airbag. In other cases, they are used as safing sensors, for example in side impact sensing arrangements. There is no hint in Matsui of using his sensors as safing sensors.
3. In many illustrations of the Matsui devices a frangible system is used. In one case, for example, a wire inside a glass tube, or a glass rod or tube which has been plated with silver, is used. In some of these cases, a sensor design is illustrated which is substantially longer that it is thick or wide. In this mailer, the sensor can extend across a significant portion of the vehicle in much the same way that the rod-in-tube sensors of the instant invention are implemented. These frangible sensors trigger by being broken, usually by means of a "Presser Member" and to thereby break an electric circuit.
As discussed below, in contrast, the sensors of this invention are not frangible and trigger by bending not by breaking.
4. Due to the requirement that tons of force are needed to trigger the Matsui sensor, rigid mounting thereof is a requirement. This is particularly important at the place on the sensor where triggering is intended to occur.
As set forth below, in contrast, the sensors of this invention trigger on bending and therefore should not in general be rigidly mounted particularly at the point where contract between the rod and tube is intended.
5. Tape switch implantation uses pressure actuated tape switches not those designed to by actuated by bending. Matsui explicitly states that the tape switch implementations disclosed are actuated by pressure (column 26, lines 20-23).
As discussed below, the sensors of the instant invention trigger on bending generally before sufficient force is available to crush the sensor.
6. The elongated sensors illustrated by Matsui are flexible lines systems, i.e., either frangible, pressure sensing tape switches, or sensors made by stretching a line or rope. All of these designs differ significantly from the rod-in-tube sensors of the instant invention. The remaining sensors disclosed are all point sensors which trigger when tons of force are applied to the sensor surface. In none of these cases is a sensor designed to be triggered by bending suggested.
7. In spite of the large potpourri of sensor designs disclosed, all of which have serious technical deficiencies, nowhere does Matsui suggest a rod-in-tube geometry of the sensor. The rod-in-tube geometry permits the sensor to be arbitrarily formed so that it covers all portions of the vehicle which are likely to be involved in a crash. In contrast, the elongated sensors of Matsui are typically shown mounted onto the bumper (erroneously designated as the fender) or immediately behind the bumper. An observation of frontal impacts shows that in approximately 30% of frontal airbag required accidents the bumper is not impacted. Thus, for these cases the Matsui sensor would not trigger.
For the purposes herein, the crush zone is defined as that part of the vehicle which crushes or deforms during a particular crash. This is a different definition from that used elsewhere and in particular in the above referenced technical papers. Also for the purposes herein, the terminology Crush Sensing Zone, or CSZ, will be used to designate that portion of the vehicle which is deformed or crushed during a crash at the sensor required trigger time. The sensor required trigger time is considered the latest time that a crash sensor can trigger for there to be sufficient time to deploy the airbag. This is determined by the airbag system designers and is a given parameter to the sensor designer for a particular crash. Naturally, there will be a different required sensor triggering time for each crash, however, it has been found, as reported in the above references, that the CSZ is remarkably constant for all crashes of the same type.
For example, the CSZ is nearly the same for all frontal barrier crashes regardless of the velocity of the crash. The same is true for 30 degree angle barrier crashes although the CSZ is different here than for frontal barrier crashes, Remarkably, and unexpectedly, it has also been found that when all frontal crashes at all different velocities are taken into account, the CSZ rearmost boundary becomes an approximate three dimensional surface lying mostly within the engine compartment of the vehicle, typically about ten to twelve inches behind the bumper at the center, and extending backward when crashes outside of the rails are considered. Finally, if a sensor is placed on this CSZ surface so that it is higher than the bumper level on the sides of the vehicle and lower in the vehicle center, as shown in FIG. 1 herein, it will do a remarkable job at discriminating between airbag required and non-deployment crashes and still trigger by the sensor required triggering time and before other sensors of comparable sensitivity. Naturally, this system is not perfect, however, it has been shown to do a better job than any other sensor system now in use.
It was this discovery which provided a basis for the subject matter described in U.S. Pat. No. 4,995,639 and then to the rod-in-tube sensor described in U.S. Pat. No. 5,441,301. During the process of implementing the rod-in-tube sensor, it was found that the same theory applies to rear impacts and that rod-in-tube sensors also have applicability to side impact sensing, although the theory is different.
In U.S. Pat. No. 5,694,320 (Breed), incorporated by reference herein, the theory of sensing rear impacts is presented and it is concluded that an anticipatory sensing system is preferred. This is because many people suffer whiplash injuries at rather low velocity impacts and if an inflatable restraint is used, the repair cost may be significant. To protect most people from whiplash injuries in rear impacts, therefore, a resetable system is preferred. The argument on the other side is that if the headrest is properly positioned, it will take care of all of the low velocity impacts and, therefore, an airbag can be used and reserved for the high velocity impacts where a crush sensing crash sensor would be used. The rod-in-tube sensor disclosed herein is, therefore, ideal for use with a deployable headrest mounted airbag for the same reasons that it is the best sensor for sensing frontal impacts. Since the rear of a vehicle typically has about one third of the stiffness of the vehicle front, electronic sensors will have even a tougher time discriminating between trigger and non-trigger cases for rear impacts. As disclosed in references 5 and 9 above, it is the soft crashes which are the most difficult for electronic sensors to sense in time.
Crush sensing crash sensors are not ideal for sensing side impacts alone, although the Volvo side impact system uses such a sensing system. This is because the sensing time is so short that there is virtually no crush (about two inches) at the time that the airbag must be deployed. Since there is very little signal out of the crush zone where electronic sensors are mounted, electronic sensors alone are not able to discriminate airbag required crashes from other crashes not requiring airbag deployment. The combination of the two sensors, on the other hand, can be used to provide a reliable determination. The crush sensor determines that there has been two inches of crush and the electronic sensor determines that the acceleration signal at that time is consistent with there being an airbag required crash. Thus, although they cannot be reliably used alone as a discriminating sensor for side impacts, the combined system does function properly.
An alternate use of the crush sensor such as the rod-in-tube sensor in side impacts is as a safing sensor. In this role, it merely determines that a crash is in progress and the main discriminating function is handled by the velocity sensing sensors such as disclosed in U.S. Pat. No. 5,231,253 (assigned to the current assignee).
Applications for the rod-in-tube crush sensing crash sensor thus include frontal, side and rear impacts, where in each case they enjoy significant advantages over all other crash sensing technologies. Examples of the preferred implementations are described in the paragraphs below.
With respect to other prior art related to the invention, Peachey (U.S. Pat. No. 4,060,705) describes a pressure actuated continuous switch which designed to actuate about its entire circumference, i.e., in all directions. The switch of the embodiment in FIG. 1 of Peachey includes a central, inner conductor 1, an insulating thread 2 helically wound around the conductor 1 and an outer conductor 3, all housed within a sheath of insulating material 4. The switch in the embodiment of FIG. 2 includes a central, inner conductor 1, an insulating thread 2 helically wound around the conductor 1, a sheath of graphite-loaded plastic 5 surrounding the thread 2, an outer conductor 3 surrounding the sheath 5 and a sheath of insulating material 4 surrounding the outer conductor 3. The switch in these embodiments is actuated when pressure is applied to the switch so that the outer conductor (FIG. 1) or sheath 5 (FIG. 2) is deflected to cause it to make contact with the inner conductor 1 and thereby establish electrical contact between the inner and outer conductors 1,3, in the embodiment of FIG. 2 through the sheath 5. In view of the helical winding of the insulating thread 2 around the inner conductor 1, these switches can be actuated by bending at almost all locations (except for an impact into a location where the insulating material 2 is interposed between the conductors 1,3.
U.S. Pat. No. 2,437,969 to Paul describes a deformable switch 10 in the form of a tube that is actuatable at all circumferential points along its length. The tube includes a central coil of electrically conducting wire 12, a braided electrically conducting, metal tube 11 and insulating separators 13 spaced at discrete locations along the length of the switch 10 to support the tube 11 around the wire 12. The switch is actuatable at all circumferential locations along the length of the tube, except for the locations at which the insulating separators 13 are located. In use, when pressure is applied to the tube 11, it deforms at the location at which pressure is applied thereby coming into contact with the wire 11 and causing a circuit to close.
U.S. Pat. No. 5,322,323 to Ohno et al. describes to a collision sensing system for an airbag including collision sensors and acceleration sensors wherein deployment of the airbag is based on a signal from the collision sensors and an analysis of the output from the acceleration sensors.